1. Field of the Invention
Example embodiments of the present invention relate to methods of removing carbonaceous impurities formed on the surface of carbon nanotubes (CNTs)
2. Description of the Related Art
Carbon nanotubes (CNTs) have been investigated due to their unique one-dimensional structure with adjustable electronic conductivity and mechanical strength. To obtain intrinsic properties of CNTs, the CNTs should be relatively pure, for example, with low quantities of or without carbonaceous impurities, for example, amorphous carbons, on their surface.
Conventional methods of preparing CNTs may include an arc-discharge process, a laser ablation process, a chemical vapor deposition (CVD) process, or a high pressure carbon monoxide process. However, regardless of the method of preparing CNTs, carbonaceous materials on their surface are the most common impurities formed during growth. Because carbon particles are more susceptible to oxidation than perfect nanotube walls, CNTs have been purified by oxidative treatments in a gas phase or liquid phase.
Conventionally, CNTs for device applications are directly grown on a pre-patterned catalyst by CVD due to its compatibility with conventional CMOS processes and deposition on large areas. However, oxidative treatments are not suitable for the purification of CNTs integrated in a device because CNTs may be lost or deformed during the oxidation process due to high reactivity or properties, for example, electrical properties may be changed. Therefore, CNTs grown by CVD are generally used without a subsequent purification process in order to avoid damages from the oxidative treatments.
Recently, CNTs have been prepared without surface carbonaceous impurities by using water vapor or ammonia gas, or by using a rapid growth process. However, the occurrence of carbonaceous impurities is inevitable during CVD.